The present invention is directed to an agitator or media mill used to grind or deagglomerate a product in a carrier medium using a grinding media and, in particular, to an improved agitator mill having an improved disc arrangement which provides an enhanced level of grinding or deagglomerating capability.
Agitator mills are used generally to disperse solids, such as pigments, in a liquid carrier medium. The dispersion is carried out by grinding and mixing in the chamber of the agitator mill, which includes an agitator shaft that is used to rotate discs or radially extending pegs in order to de-aggregate or de-agglomerate the solids to be dispersed in the liquid. The shaft is generally driven by a mechanical device such as a motor. A grinding media, such as silica or the like, is placed in the agitator mill chamber and is used in connection with the discs or radially extending pegs to disperse the solid material in the liquid. After the grinding and mixing of the solids and liquid is complete, it is necessary to separate the mixture from the grinding media, and then to discharge the mixture from the milling chamber.
One such separator arrangement is described in U.S. Pat. No. 5,333,804, which is assigned to the assignee of the present invention, and is incorporated by reference as if fully set forth. This patent describes a prior known type of disc mill over which the present invention provides improved performance. An example of a known agitator mill utilizing axially extending pins located on the rotor which travel in spaces between fixed pins extending inwardly into the milling chamber is shown in U.S. Pat. No. 4,620,673 which is also incorporated herein by reference as if fully set forth. The two different types of mills (the disc mill and the axially extending pin mill) perform similarly in use.
In prior known disc mills, generally circular mixing discs are mounted on the drive shaft. The discs may be provided with arcuate slots in order to increase the pumping action of the liquid slurry and the grinding media. It has also been known to utilize a solid disc with radially extending bumps that extend from the inner periphery of the disc to the outer periphery in order to increase pumping and the impact force of the grinding media in a mill. Prior mills have also utilized axially and radially spaced apart arms or blades that extend radially from the agitator shaft, with pin-shaped activator elements extending from one or both sides of the arms.
It would be desirable to provide an agitator mill with an improved disc arrangement to improve mill performance in mixing or dispersing solids into a liquid carrier medium, for example by reducing the time required to reduce the particle size of the solid to a desired range and/or by providing the ability to produce a reduced particle size in comparison to the known prior art mills.
The present invention provides an agitator with a rotatable axial shaft with a plurality of grinding discs connected generally perpendicular to the shaft. At least one grinding disc has an axially extending pin spaced radially outwardly from the shaft and radially inwardly from a peripheral edge of the disc, which is aligned with a smooth surface on a next adjacent disc.
In another aspect, the present invention provides an improved disc for use in connection with an agitator or fine media mill which includes at least one axially extending pin located in proximity to the disc periphery.